Since it is so small & easily lost, and used so infrequently, I kept the little key on a 6 inch loop of bright yarn/string and then put in the ziplock bag that I use for keeping my brevet card and receipts from controls (and my
dental retainer that cost a $1000!). While riding, that ziplock bag is in a bento box bag on the top tube. When leaving the bike locked, I take that ziplock bag with me and keep it in a zipped pant pocket.